// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/process/internal_linux.h"

#include <limits.h>
#include <unistd.h>

#include <map>
#include <string>
#include <vector>

#include "base/files/file_util.h"
#include "base/logging.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_split.h"
#include "base/strings/string_util.h"
#include "base/threading/thread_restrictions.h"
#include "base/time/time.h"

namespace base {
namespace internal {

    const char kProcDir[] = "/proc";

    const char kStatFile[] = "stat";

    FilePath GetProcPidDir(pid_t pid)
    {
        return FilePath(kProcDir).Append(IntToString(pid));
    }

    pid_t ProcDirSlotToPid(const char* d_name)
    {
        int i;
        for (i = 0; i < NAME_MAX && d_name[i]; ++i) {
            if (!IsAsciiDigit(d_name[i])) {
                return 0;
            }
        }
        if (i == NAME_MAX)
            return 0;

        // Read the process's command line.
        pid_t pid;
        std::string pid_string(d_name);
        if (!StringToInt(pid_string, &pid)) {
            NOTREACHED();
            return 0;
        }
        return pid;
    }

    bool ReadProcFile(const FilePath& file, std::string* buffer)
    {
        buffer->clear();
        // Synchronously reading files in /proc is safe.
        ThreadRestrictions::ScopedAllowIO allow_io;

        if (!ReadFileToString(file, buffer)) {
            DLOG(WARNING) << "Failed to read " << file.MaybeAsASCII();
            return false;
        }
        return !buffer->empty();
    }

    bool ReadProcStats(pid_t pid, std::string* buffer)
    {
        FilePath stat_file = internal::GetProcPidDir(pid).Append(kStatFile);
        return ReadProcFile(stat_file, buffer);
    }

    bool ParseProcStats(const std::string& stats_data,
        std::vector<std::string>* proc_stats)
    {
        // |stats_data| may be empty if the process disappeared somehow.
        // e.g. http://crbug.com/145811
        if (stats_data.empty())
            return false;

        // The stat file is formatted as:
        // pid (process name) data1 data2 .... dataN
        // Look for the closing paren by scanning backwards, to avoid being fooled by
        // processes with ')' in the name.
        size_t open_parens_idx = stats_data.find(" (");
        size_t close_parens_idx = stats_data.rfind(") ");
        if (open_parens_idx == std::string::npos || close_parens_idx == std::string::npos || open_parens_idx > close_parens_idx) {
            DLOG(WARNING) << "Failed to find matched parens in '" << stats_data << "'";
            NOTREACHED();
            return false;
        }
        open_parens_idx++;

        proc_stats->clear();
        // PID.
        proc_stats->push_back(stats_data.substr(0, open_parens_idx));
        // Process name without parentheses.
        proc_stats->push_back(
            stats_data.substr(open_parens_idx + 1,
                close_parens_idx - (open_parens_idx + 1)));

        // Split the rest.
        std::vector<std::string> other_stats = SplitString(
            stats_data.substr(close_parens_idx + 2), " ",
            base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
        for (size_t i = 0; i < other_stats.size(); ++i)
            proc_stats->push_back(other_stats[i]);
        return true;
    }

    typedef std::map<std::string, std::string> ProcStatMap;
    void ParseProcStat(const std::string& contents, ProcStatMap* output)
    {
        StringPairs key_value_pairs;
        SplitStringIntoKeyValuePairs(contents, ' ', '\n', &key_value_pairs);
        for (size_t i = 0; i < key_value_pairs.size(); ++i) {
            output->insert(key_value_pairs[i]);
        }
    }

    int64_t GetProcStatsFieldAsInt64(const std::vector<std::string>& proc_stats,
        ProcStatsFields field_num)
    {
        DCHECK_GE(field_num, VM_PPID);
        CHECK_LT(static_cast<size_t>(field_num), proc_stats.size());

        int64_t value;
        return StringToInt64(proc_stats[field_num], &value) ? value : 0;
    }

    size_t GetProcStatsFieldAsSizeT(const std::vector<std::string>& proc_stats,
        ProcStatsFields field_num)
    {
        DCHECK_GE(field_num, VM_PPID);
        CHECK_LT(static_cast<size_t>(field_num), proc_stats.size());

        size_t value;
        return StringToSizeT(proc_stats[field_num], &value) ? value : 0;
    }

    int64_t ReadProcStatsAndGetFieldAsInt64(pid_t pid, ProcStatsFields field_num)
    {
        std::string stats_data;
        if (!ReadProcStats(pid, &stats_data))
            return 0;
        std::vector<std::string> proc_stats;
        if (!ParseProcStats(stats_data, &proc_stats))
            return 0;
        return GetProcStatsFieldAsInt64(proc_stats, field_num);
    }

    size_t ReadProcStatsAndGetFieldAsSizeT(pid_t pid,
        ProcStatsFields field_num)
    {
        std::string stats_data;
        if (!ReadProcStats(pid, &stats_data))
            return 0;
        std::vector<std::string> proc_stats;
        if (!ParseProcStats(stats_data, &proc_stats))
            return 0;
        return GetProcStatsFieldAsSizeT(proc_stats, field_num);
    }

    Time GetBootTime()
    {
        FilePath path("/proc/stat");
        std::string contents;
        if (!ReadProcFile(path, &contents))
            return Time();
        ProcStatMap proc_stat;
        ParseProcStat(contents, &proc_stat);
        ProcStatMap::const_iterator btime_it = proc_stat.find("btime");
        if (btime_it == proc_stat.end())
            return Time();
        int btime;
        if (!StringToInt(btime_it->second, &btime))
            return Time();
        return Time::FromTimeT(btime);
    }

    TimeDelta ClockTicksToTimeDelta(int clock_ticks)
    {
        // This queries the /proc-specific scaling factor which is
        // conceptually the system hertz.  To dump this value on another
        // system, try
        //   od -t dL /proc/self/auxv
        // and look for the number after 17 in the output; mine is
        //   0000040          17         100           3   134512692
        // which means the answer is 100.
        // It may be the case that this value is always 100.
        static const int kHertz = sysconf(_SC_CLK_TCK);

        return TimeDelta::FromMicroseconds(
            Time::kMicrosecondsPerSecond * clock_ticks / kHertz);
    }

} // namespace internal
} // namespace base
